Composition and process for cleaning and coating metal surfaces



United States Patent 3,450,577 COMPOSITION AND PROCESS FOR CLEANING AND COATING METAL SURFACES James R. Beach, Detroit, Mich., assignor to Hooker Chemical Corporation, Niagara Falls, N.Y., a corporation of New York No Drawing. Filed Nov. 5, 1965, Ser. No. 506,573 Int. Cl. C23f 7/10; C23g 1/00 US. Cl. 1486.15 10 Claims ABSTRACT OF THE DISCLOSURE A cleaner-coater concentrate composition for treating ferrous metal surfaces which contains an alkali metal phosphate, a sugar, fluoride ions, molybdate ions, oxalate ions, ferric ions, and a low-foaming wetting agent. Desirably, the components of the composition are monosodium phosphate, succrose, sodium bifluorjtl ammonium molybdate, oxalic acid, and erric oxalate? This concentrate composition is desiraby ormed into an aqueous treating solution containing from about 1 to 10 pounds of concentrate per hundred gallons of solution and is effective in cleaning oil or light soil from ferrous metal surfaces and forming on the surface an attractive iron phosphate protective and/or paint-base coating.

This invention relates to a novel composition and process for cleaning and coating metal surfaces and more particularly, it relates to a composition and process suitable for cleaning ferrous metal surfaces and forming thereon a phosphate coating.

It has long been common in the art to treat metal surfaces to form a protective phosphate coating on the surface. In many instances, zinc phosphate or mixed zinciron phosphate coatings are used because they provide an excellent corrosion-resistant, paint-base coating. Frequently, however, the degree of corrosion protection provided by such phosphate coatings is not required. This has been found to be particularly true where the treated metal is used in applications where resistance to salt spray is not an important factor. In such instances, the additional cost of the zinc phosphate or mixed zinc-iron phosphate coatings is often difiicult to justify, notwith standing the improved corrosion protection which they provide.

It has, therefore, become the practice to utilize coating materials which produce an iron phosphate coating on the metal surface for many of these applications. Typically, the surfaces treated are iron or steel surfaces and the coating composition is an aqueous solution of an alkali metal phosphate. Although the corrosion resistance of the coatings thus-produced is not as great as that obtained with a zinc phosphate coating, the cost savings realized in using these coatings more than make up for this, particularly where salt spray corrosion is no problem. Although coatings of this type have generally been found to be quite satisfactory for the purpose intended, some difliculties have been encountered both with respect to the application thereof and the properties of the coating produced.

One of the problems which has heretofore been encountered is that of producing a dust-free coating. Additionally, coating solutions of this type have frequently required a relatively close control of the process operating conditions and have been useful over only a relatively narrow pH range. Moreover, coatings of this type which have been produced by the prior art processes have often been unattractive, from a visual standpoint, thus detracting from their salability.

3,450,577 Patented June 17, 1969 It is, therefore, an object of the present invention to provide an improved coating composition for producing visually attractive, dust-free iron phosphate coatings on metal surfaces.

Another object of the present invention is to provide an improved coating composition which is effective in cleaning the metal surfaces to remove dirt, oil, and other light soil from the metal surface during the coating operation.

A further object of the present invention is to provide an improved process for forming an iron phosphate coating on metal surfaces, which process is easily controlled and may be operated over a relatively wide pH range.

These and other objects will become apparent to those skilled in the art from a description of the invention which follows.

Pursuant to the above objects, the present invention includes a cleaning-coating concentrate composition which comprises an alkali metal phosphate, a sugar, fluoride ions, molybdate ions, oxalate ions, ferric iron ions, and a low-foaming wetting agent. When iron or steel is treated with an aqueous solution formed from. the above concentrate, oil, grease and other similar light surface soil are removed from the metal and there is formed thereon an attractive dust-free, iron phosphate coating.

More specifically, in the practice of the present invention, the cleaner-coater concentrate is comprised of an alkali metal phosphate selected from the group consisting of mono-, di-, and tri-alkali metal phosphates. It is to be appreciated, that as used in the specification and claims, the term alkali metal" is intended to refer to sodium, potassium, lithium, cesium, and rubidium. Of these, the preferred alkali metal is sodium and, for this reason, specific reference will be made hereinafter to this material. This is not, however, to be taken as a limitation of the present invention because other alkali metals are also useful and phosphates of these, as well as sodium compounds alone or in mixture, may be used in the composition and process of the present invention.

Of the alkali metal phosphates indicated hereinabove as being useful in the composition of the present invention, the preferred alkali metal phosphate is monosodium phosphate. Desirably, this material, or other alkali metal phosphates which may be used, are present in the composition in an amount at least 50% by weight of the concentrate composition. Amounts of the alkali metal phosphate within the range of about 50 to about 96% by weight of the concentrate composition are typical, with amounts within the range of about 65 to about 92% by weight of the concentrate composition being preferred.

The sugar portion of the concentrate composition of the present invention is desirably a disaccharide, such as sucrose. Exemplary of disaccharides, other than sucrose which may be used are maltose, lactose and the like. Additionally, in some instances, monosaccharides, such as glucose, mannose, fructose, and the like, may also be used. Of these sugars, the regular commercial grade of the sugar has been found to be satisfactory for use in the present composition. Typically, the sugar is present in the composition in an amount within the range of about 1 to about 10% by weight of the concentrate composition and preferably in an amount within the range of about 2 to 8% by weight.

The flouride ions in the cleaner-coater composition of the present invention are desirably added as a water dispersible or soluble fluoride or bifluoride. Typical of such compounds are hydrofluoric acid, the alkali metal fluorides and bifluorides, such as sodium fluoride and sodium bifluoride, although other water soluble fluorides or bifluorides, such as those of ammonia and the like,

may also be used. In many instances, the preferred fluoride compound for inclusion in the present composition has been found to be sodium bifluoride. Typically, the fluoride ions, calculated as sodium bifluoride, are present in the concentrate composition in proportion within the range of about 1 to about 10% by weight and preferably, within the range of about 2 to about 8% by weight.

The molybdate ions are preferably added to the present compositions in the form of a water dispersible or water soluble molybdate. Exemplary of such compounds which may be used are molybdic acid, the alkali metal molybdates, ammonium molybdate, and the like, of which, ammonium molybdate has been found, in many instances, to be preferred. Typically, the molybdate ions, calculated as ammonium molybdate, are present in the concentrate composition in a proportion within the range of about 0.1 to about by weight of the composition and preferably within the range of about 0.5 to about 3% by weight.

The oxalate ions are desirably added to the cleanercoater composition of the present invention in the form of oxalic acid. Other water dispersible or water soluble oxalates, such as the alkali metal or ammonium oxalates may be used. Additionally, the oxalate ions may be incorporated in the composition as ferric oxalate, thus providing for the inclusion of both oxalate ions and ferric iron ions by the addition of a single compound. Typically, the oxalate ions, calculated as oxalic acid, are present in the composition in proportion within the range of about 0.5 to about by weight of the concentrate composition and are preferably within the range of about 1 to about 5% by weight of the composition.

As has been indicated hereinabove, the ferric iron ions which form a part of the present composition may be added as the ferric oxalate. Additionally other ferric ion compounds which are dispersible and/ or soluble in water may also be used. Exemplary of such compounds which may be used are ferric nitrate, ferric chloride, ferric sulfate, ferric hydroxide, and the like. Typically, the ferric ions, calculated as ferric oxalate, are present in the composition in an amount within the range of about 0.1 to about 3% by weight of the concentrate composition, with amounts within the range of about 0.2 to about 2% by weight of the composition being preferred.

The low foaming wetting agent is desirably present in the cleaner-coater concentrate composition in a proportion within the range of about 1 to about 12% by weight of the composition and preferably constitutes about 2 to about 9% by weight of the composition. Various wetting agents of the low foaming type, including anionic, cationic and nonionic wetting agents may be used, although the nonionics are preferred. Biodegradable forms of these wetting agents may be used. The low foaming wetting agents may be of various types, such as fatty ester sulfates, aliphatic polyethers, polyoxyethylene esters of fats and oils such as vegetable oils, organic polyphosphate esters, amine alkyl phenol polyglycol ethers, modified amides, alkylaryl sulfonates, amine polyglycol condensates, alkylaryl polyethers, ethoxylated tall oil, polyoxyethylene ethers, alkylpoly(ethyleneoxide) alcohols, and the like, as are known in the art. Typically, in these materials the aryl group is phenyl or napthyl, the alkyl group contains from about 2 to 20 carbon atoms and when alkoxylated they contain from about 2 to moles of the alkylene oxide, such as ethylene oxide or propylene oxide.

In formulating the working solution for treating iron and steel surfaces in accordance with the method of the present invention, the concentrate composition is dissolved or dispersed in water so as to provide a working solution having the desired concentration. Typical concentrations which may be used are within the range of about 1 to about 10 pounds of the concentrate per 100 gallons of working solution with concentrations within the range of about 3 to about 8 pounds per hundred gallons of working solution being preferred.

The iron or steel surface to be treated is then contacted with this aqueous solution for a period of time sufficient to effect cleaning of the surface and the formation thereon of the desired iron phosphate coating. Desirably, the treating solution is sprayed onto the metal surface although, other contacting techniques, such as immersion, and the like, may also be used. Typical contact times, when using spray application techniques, are from about 5 seconds up to about 5 minutes, with contact times within the range of about 0.5 to about 2 minutes being preferred. It has been found to be beneficial that the treating solution is at an elevated temperature, desirably above about 55 degrees centigrade. Preferably, the treating solution is at a temperature within the range of about 60 to about degrees centigrade, although in some instances higher temperatures, e.g., centigrade, may be used.

In carrying out the process of the present invention, the iron or steel surfaces to be treated are contacted with the hot aqueous treating solution, as was mentioned above. In view of the ability of the treating solutions of the present invention to remove oil, grease, and similar light soil from the surface of the metal to be treated, a separate cleaning step, prior to the application of the subject treating solution, is normally not required. Where, however, the surfaces to be treated have thereon oxide coatings, carbonaceous smut, or similar difficulty removable materials, an alkaline or acid pre-cleaning step may be used. Generally, such additional cleaning operation has not been found to be necessary. Following the contact of the metal surface with the present treating solution, the thuscoated surface is desirably rinsed with water, preferably hot water at a temperature above about 50 centigrade. Rinsing times of from 10 seconds to two minutes are typical with times within the range of about 0.5 to 1 minute being preferred. Thereafter, if desired, the waterrinsed surface may be given a further rinse, preferably with a dilute solution containing hexavalent chromium. Such solution may contain from about 0.03 to about 0.8% hexavalent chromium, calculated as CrO such as a dilute cromic acid solution. Additionally other sources of hexavalent chromium may be used, such as the alkali metal and ammonium chromates and dichromates and dichromates of heavy metals, such as Zn, Ca, Cr, Fe, Mg, and Al and the like. This rinse solution may be utilized at room temperature or at an elevated temperature, temperatures and times above about 55 centigrade and from 10 seconds to two minutes being typical, with temperatures and times within the range of about 60 to 75 degrees centigrade and 0.5 to 1 minute respectively, being preferred. After drying, either at room temperature or at an elevated temperature sufficient to drive off surface moisture, e.g., l00200 degrees centigrade, the thus-rinsed surface may then be given a suitable protective coating, such as paint or the like.

By the process of the present invention there is provided a simple and economical treatment for iron and steel surfaces which provides a uniform dust-free, iron phosphate coating which has an attractive dark blue color and which provides an excellent base for paint and other protective coating materials. It has been found that the coating produced permits excellent coverage with only a low film thickness of most paints. Additionally, the process is easily controlled so that effective coatings are produced over a wider pH range'of operation then has theretofore been possible with coating solutions of this type. Moreover, mild steel or black iron equipment can be used, and sludge formation is at a minimum.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. It is to be appreciated that these examples are intended to be exemplary of the compositions and processes of the present invention and are not to be taken as limitations thereof. In these examples, unless otherwise indicated, temperatures are given in degrees centigrade and parts and percents are by weight. Additionally, in the tests to which the coated and painted panels are subjected, the rating is on a scale of 0-10, 0 indicating poorest performance and indicating best.

Example 1 A concentrate composition was formulated containing the following components in the amounts indicated:

Components: Parts by weight Monosodium phosphate 80.5 Commercial sugar (sucrose) Sodium bifluoride Ammonium molybdate 1.0 Oxalic acid Ferric oxalate Low foaming wetting agent (aliphatic polyether formed by ethoxylation of oxyalcohol) 6.0

An aqueous treating solution was formulated by dissolving the above concentrate in water to form a solution containing 6 pounds of concentrate per 100 gallons of treating solution. This solution, at a temperature of about 70 degrees centigrade was sprayed for 1 minute on 4 inch by 12 inch, 24-gauge cold-rolled steel panels, having a light oil coating. Thereafter, the panels were rinsed for 30 seconds in hot 'water, immersed for 30 seconds in a dilute aqueous solution of chromic acid containing 0.1% by weight Cr", calculated as CrO at about 20 degrees centigrade and thereafter dried in an oven at about 190 centigrade. The coating weight on the panels treated was found to be in the range of about 17 to 21 milligrams per square foot and the coating was an attractive dust-free, dark blue, iron phosphate. Thereafter, commercial alkyd, and epoxy paints were applied to the phosphate coated panels and these panels were subjected to the 100% humidity test, conical mandrel and impact physical tests and knife blade adhesion test. After 168 hours in the 100% humidity test, the panels had a rating of from 9 to 10, while in the conical mandrel; impact, both concave and convex; and knife adhesion test, ratings of 10 were obtained in each for all of the panels, as compared to similar painted bare steel panels which had a rating in the humidity test of 6-9.

Example 2 The procedure of Example 1 was repeated with the exception that the cleaner-coater solution used was formulated from a concentrate having the following components in the amounts indicated:

Components:

Monosodium phosphate Commercial grade sugar (sucrose) 10 Ammonium bifluoride 8.3 Ammonium molybdate 7.5 Sodium oxalate 7.5 Ferric oxalate 0.7 Low foaming wetting agent as in Example 1 6.0

Panels treated with this coating solution, as in Example 1, were found to have a uniform, dust-free, blue coating which was very attractive in appearance.

Example 3 Parts by weight same resuts in substantially the same or equivalent manner, it being intended to cover the invention broadly, in whatever form its principle may be utilized.

What is claimed is:

-1. A concentrate composition useful in forming an aqueous solution for treating metal surfaces which comprises an alkali metal phosphate in an amount of from about 50 to 96% by weight, sugar in an amount of from about 1 to 10% by weight, fluoride ions, calculated as sodium bifluoride, in an amount of from about 1 to 10% by weight, molybdate ions, calculated as ammonium molybdate, in an amount of from about 0.1 to 5% by weight, oxalate ions, calculated as oxalic acid, in an amount of from about 0.5 to 10% by weight, ferric ions, calculated as ferric oxalate, in an amount of from about 0.1 to 3% by weight, and a low-foaming wetting agent in an amount of from about 1 to- 12% by weight.

2. The composition as claimed in claim 1 wherein the alkali metal phosphate is a mono-alkali metal phosphate.

3. The composition as claimed in claim 2 wherein the monoalkali metal phosphate is monosodium phosphate, the sugar is sucrose, the fluoride ions are added as bifluoride, the molybdate ions are added as ammonium molybdate, the oxalate ions are added as oxalic acid and the ferric iron ions are added as ferric oxalate.

4. An aqueous solution, useful in treating metal surfaces to provide a protective and/or paint-base coating thereon, which comprises water and the concentrate composition as claimed in claim 1.

5. The aqueous treating solution as claimed in claim 4 wherein the concentrate composition is present in the treating solution in an amount within the range of about 1 to 10 pounds per 100 gallons of treating solution.

6. The treating solution as claimed in claim 5 wherein the alkali metal phosphate is monosodium phosphate, the sugar is sucrose, the fluoride ions are added as sodium bifluoride, the molybdate ions are added as ammonium molybdate, the oxalate ions are added as oxalic acid, and the ferric iron ions are added as ferric oxalate.

7. A process for treating ferrous metal surfaces to provide a protective and/or paint base coating thereon which comprises contacting the surface to be treated with the aqueous treating solution as claimed in claim 4.

8. The proces as claimed in claim 7 wherein the aqueous treating solution contains the concentrate composition in an amount within the range of about 1 to 10 pounds per 100 gallons of treating solution.

9. The method as claimed in claim 8 wherein in the concentrate composition the alkali metal phosphate is monosodium phosphate, the sugar is sucrose, the fluoride ions are added as sodium bifluoride, the molybdate ions are added as ammonium molybdate, the oxalate ions are added as oxalic acid, and the ferric iron ions are added as ferric oxalate.

10. A ferrous metal surface having formed thereon a substantially dust-free iron phosphate coating, which coating is formed on the surface in accordance with the method of claim 9.

References Cited UNITED STATES PATENTS 1,514,494- 11/1924 Williams 148-615 1,895,569 1/1933 Curtin 1486.15 X 2,809,906 10/1957 Baecke'r et a1. 148-614 2,832,707 4/1958 Rossteytscher l486.l4 2,854,370 9/ 1958 Kronstein 148--6.15

RALPH S. KENDALL, Primary Examiner.

US. Cl. X.R.

l48-6.l6; 252l36, 147 

